1. Field of the Invention
The present invention relates to a hydraulic control device of an automatic transmission, wherein a pressure regulator valve is used for regulating a pressure of oil delivered from an oil pump, into a line pressure.
2. Description of the Prior Art
A known example of hydraulic control device of an automatic transmission is disclosed in Japanese laid-open Patent Publication No. 57-40147. This hydraulic control device was developed to solve a problem that air is sucked into an oil strainer when the oil level in an oil reservoir is lowered due to a low oil temperature, and the air is mixed into the oil flowing into an inlet oil path. In the hydraulic control device disclosed in the above-identified publication, a drain port of a pressure regulator valve communicates with a portion of an inlet oil path which is located downstream of the oil strainer, so that the oil drained from the pressure regulator valve is directly led to an inlet port of an oil pump without passing through the oil strainer.
In the known device, however, the oil discharged from the drain port of the pressure regulator valve flows in a direction which is reverse to a direction in which the oil flows from an opening of the oil strainer toward the inlet oil path, resulting in a collision of flows of the oil.
To solve the above problem, it has been proposed in Japanese laid-open Patent Publication No. 6-272762 to provide a baffle member 40 as shown in FIG. 7, so that the direction 48 of flow of the oil discharged from a drain port 10c of a pressure regulator valve 11 coincides with the direction 46 of the oil flowing from an oil strainer 34 toward an inlet port 20a.
In the hydraulic control device of the automatic transmission disclosed in Japanese laid-open Patent Publication No. 6-272762 as identified above, however, the pressure regulator valve 11 having the drain port 10c, oil strainer 34 having an opening 34a, and the inlet oil path 10e that communicates with the inlet port 20a of the oil pump are provided in the same valve body 10. Accordingly, the position at which the pressure regulator valve 11 can be installed is limited to a region located between the opening 34a of the oil strainer and the inlet oil path 10e.
As shown in FIG. 8, the drain port 10c of the pressure regulator valve 11 must be formed at a position covered by the oil strainer 34, namely, between the opening 34a of the strainer and the inlet oil path 10e. Since the pressure regulator valve and the oil strainer are formed in the same valve body, the positions of other ports of the pressure regulator valve are determined to be within a region (delimited by a one-dot chain line) covered by the strainer once the position of the drain port 10c is determined.
When a large number of valves are mounted in the valve body, therefore, there is a limit to the layout of the valves since the position of the pressure regulator valve cannot be freely varied. Also, once the position of the drain port is determined, the shape of the oil strainer cannot be freely selected or determined.